System for lighting a fluorescent lamp

ABSTRACT

A system for instantaneously lighting a fluorescent lamp is disclosed which includes a capacitor, a pulse transformer having primary and secondary windings, and a diode and silicon symmetrical switch which are connected in parallel with said primary winding and said capacitor. The said primary winding, diode, capacitor and silicon symmetrical switch form an oscillatory circuit for applying a unidirectional pulse series across the fluorescent lamp, thereby instantaneously lighting the lamp. The circuit is composed entirely of components of a small size, facilitating the production of miniature fluorescent lamp appliances.

United States Batent 3,525,901 8/1970 Sammis Inventor Masayoshi Mlyajima Kyoto, Japan Appl. No. 3,367

Filed Jan. 16, 1970 Patented Dec. 28, 1 971 Assignee Kuroi Electric Industrial Company Kyoto, Japan SYSTEM FOR LIGHTING A FLUORESCENT LAMP 4 Claims, 4 Drawing Figs.

U.S. Cl 315/94, 307/305, 315/98, 315/105, 315/ 107, 315/260, 315/276 Int. Cl 11051: 39/00 Field of Search 315/94, 98, 105, 107, 260, 262, 276, 100 U; 307/305 References Cited UNITED STATES PATENTS 2,458,277 l/1949 Lark et al. 315/262 X 3,476,976 11/1969 Morita et a1. 315/105 FOREIGN PATENTS 1,119,874 7/1968 Great Britain 315/105 Primary Examinerl-lerman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney- Pendleton, Neuman, Williams and Anderson ABSTRACT: A system for instantaneously lighting a fluorescent lamp is disclosed which includes a capacitor, a pulse transformer having primary and secondary windings, and a diode and silicon symmetrical switch which are connected in parallel with said primary winding and said capacitor. The said primary winding, diode, capacitor and silicon symmetrical switch form an oscillatory circuit for applying a unidirectional pulse series across the fluorescent lamp, thereby instantaneously lighting the lamp. The circuit is composed entirely of components of a small size, facilitating the production of miniature fluorescent lamp appliances.

SYSTEM FOR LIGHTING A FLUORESCENT LAMP FIELD OF THE INVENTION The invention is directed to a starting circuit for a fluorescent lamp, and more particularly to a circuit utilizing components of a reduced size which provides instantaneous lighting of the fluorescent lamp.

BACKGROUND OF THE INVENTION A fluorescent lamp which starts instantaneously, without requiring an extended warmup period and without undue flickering, has long been a desirable commercial commodity. Some quick starting fluorescent lamps have been designed in corporating an auxiliary electrode located between the cathodes, at a considerable increase in the price of the lamp itself. Starting circuits to instantly light a fluorescent lamp have also incorporated high impedance inductors to generate the flashover voltage required to light the lamp. Such circuits, however, are too bulky and too costly to be practical.

At the present time the greatest reduction in size of lamp starting circuits has been achieved through the use of a glow lamp, which has a voltampere characteristic which is used to provide the required flashover voltage between the lamp cathodes. However, glow lamps have a relatively short useful life, making them both uneconomical and undesirable from the consumer point of view.

SUMMARY OF THE INVENTION The invention is directed to a starting circuit for a miniature fluorescent lamp of the instant-lighting type. The circuit incorporates a conventional fluorescent lamp and stabilizer and adds a starting circuit consisting of parts of small size which oscillate at high frequency. The elements are in fact so miniaturized that they may be packaged within a small casing of the same size as a glow lamp. Further, the starting circuit of this invention may be directly substituted for the glow lamp of prior art circuits, resulting in an economical miniature fluorescent lamp appliance having a long operating lifetime. The glow lamp used in prior art quick-starting circuits is eliminated, resulting in long life for the starting circuit and economical operation. The large and heavy stabilizer used in prior art circuits is also eliminated.

The starting circuit includes a diode, an autotransformer and an oscillatory circuit which convert the voltage from a conventional AC power source to a unidirectional pulse voltage series to provide the voltage required to trigger a fluorescent lamp. The oscillatory circuit includes a capacitor coupled in series with a primary winding of the autotransformer and a diode and silicon symmetrical switch in parallel with this series combination to generate a series of unidirectional voltage pulses of sufficient amplitude to quickly light the fluorescent lamp.

IN THE DRAWINGS FIG. I is a schematic circuit diagram of a specific embodiment of the starting circuit of the present invention.

FIG. 2 is a sectional view of a container which encases the elements of the starting circuit of the present invention.

FIG. 3'is an illustration of the insertion of the starting circuit container shown in FIG. 2 in a socket for a glow lamp.

FIG. 4 is a waveform of one complete cycle of the pulse current wave generated by the starting circuit of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, which is a schematic diagram of a circuit embodying this invention, a conventional fluorescent lamp 1 is shown having cathodes 2 and 3, each cathode having two legs. A leg 4 of cathode 2 is coupled to a terminal 5 of conventional 120 volt AC power source 6. A radiofrequency stabilizing choke 8 is coupled in series between a leg 9 of cathode 3 and a second terminal 10 of power source 6. The winding of stabilizer 10, in

an alternative embodiment (not shown) may be bisected, and the bisected windings connected separately in series with the terminals 5 and 10 of AC power supply 6 for more effective elimination of radiofrequency interference. The AC power supply 6 supplies the necessary voltage to maintain the fluorescent lamp in a lighted condition. However, a voltage much greater than the supply voltage is required to produce the initial flashover through the inert gas filling the space between cathodes 2 and 3 of fluorescent tube 1. A specific embodiment of the starting circuit 12 of this invention which produces an almost immediate flashover between the cathodes 2 and 3 and thus instantaneous lighting of lamp 1 will now be described.

The starting circuit 12 of this invention includes a pulse transformer 14 having an autotransformer configuration, the primary winding 16 and a secondary winding 18 being connected in series and wound on a common core 20, indicated schematically. A diode 22 is connected in series between the secondary winding 18 and a leg 24 of cathode 2 of lamp 1. A capacitor 26 is connected in series between the primary winding 16 of autotransformer 14 and a leg 28 of lamp cathode 3. A series combination of a silicon symmetrical switch 30 and a diode 32 is connected in parallel with the series combination primary winding 16 and capacitor 26. The diodes 22 and 32 have a polarity such that both conduct in the same direction. A suitable silicon symmetrical switch for use in the starting circuit of this invention is the DIAC bidirectional trigger switch manufactured by General Electric. The switch is a twoterminal device which is triggered to a one-directional low impedance state by increasing the voltage applied across its terminals beyond a predetermined switching value. Once the switching device is triggered to the low impedance state, the state persists so long as the applied voltage is sufficient to insure the flow of a predetermined sustaining current through the body of the element. In the circuit of this invention this means that the device will maintain its low impedance state until near the end of the half-cycle of applied line voltage which caused the triggering action.

The circuit operates in the following manner, reference also being made to FIG. 4 which illustrates graphically a complete cycle of the pulse current wave generated by the starting circuit of this invention. An AC voltage source 6 is coupled to input terminals 5, 10. When the AC voltage is in a half-cycle such that diode 22 is reverse biased, the diode 22 presents a very high impedance to any current flow in the circuit, preventing the charging of capacitor 26 and thereby preventing the voltage applied to silicon switch 30 from reaching its threshold voltage. In the circuit of FIG. 1, this condition occurs when terminal 10 is positive with respect to terminal 5. Consequently, during this half-cycle there can be no voltage pulse applied across the lamp cathodes.

During the half-cycle when the polarity reverses and terminal 5 is positive with respect to terminal 10, current starts to fiow through the series circuit including lamp cathodes 2 and 3, the series connected windings of pulse transformer 14, capacitor 26 and diode 22, the diode now being forwardbiased. The current is very small, being only the charging current for capacitor 10. When the AC voltage applied to the silicon symmetrical switch 30 reaches the switch threshold level, the switch turns on and current now flows through a series circuit including diode 22, autotransformer secondary l8, diode 32 (which is forward biased during this input voltage half-cycle), switch 30 and lamp cathodes 2 and 3. Further, the capacitor 26, having been continuously charged until the threshold or tum-on voltage of the silicon switch 30 is reached, now discharges through the closed circuit including autotransformer primary winding 16, diode 32 and switch 30. These elements comprise an oscillatory circuit whose fundamental frequency is determined by capacitor 26 and transformer primary winding 16. The current flow through primary winding 16 of transformer 14 is illustrated in FIG. 4, which illustrates the waveform of a single cycle of pulse current. When peak current Ipl,40, flows through the primary winding 16, a boosted voltage pulse is generated across secondary 18 of transformer 8. Because both diodes 22 and 32 are forward biased during this half-cycle, and because switch 30 is turned on, the secondary winding 18 is effectively coupled across lamp 1, supplying a boosted cathode current to cathodes 2 and 3 promoting the release of free electrons (thermal electrons) from the cathode and a voltage flashover within the fluorescent lamp. The resulting current flow through the series branch including switch 30 is unidirectional as governed by the polarity of diode 32; thus oscillation ceases abruptly with the end of capacitor discharge. The current flow within the primary winding 16 rapidly approaches a null after the end of capacitor discharge lp2,42 as shown in FIG. 4.

As the capacitor discharges during each pulse cycle, the voltage applied to the silicon switch decreases and the current flow through switch 30 falls below the value required to maintain the switch in the low impedance state. Thus the voltage applied to switch 30 falls below the voltage required to maintain the switch in the conducting state and the switch returns to the high impedance state.

The switch is turned on only during a half-cycle of each full cycle of applied line voltage. The polarity of diodes 22 and 32 prevents the switch from being turned on during the other half-cycle. Thus the starting circuit as exemplified by the specific embodiment disclosed herein generates a series of unidirectional voltage pulses of a magnitude and duration sufficient to instantaneously light the fluorescent lamp. During the many rapid repetitions of the above cycle, the cathodes of the fluorescent lamp are heated, electron discharge starts and flashover between the lamp cathodes occurs. The time interval between the application of AC power and beginning of discharge is between 0.3 and 1 second.

Further, this stable series of starting pulses prevents burning and blackening of the cathodes of the fluorescent lamp at the start of discharge and thus lengthens the lifetime of the fluorescent lamp. Moreover, the use of the circuit of this invention to generate a unidirectional pulse series prevents the occurrence of resonance noise which might otherwise be generated by stabilizer 8 and capacitor 26, and removes a major source of radiofrequency interference.

As shown in FIG. 2, the miniaturized components of the starting circuit of this invention may be encased in a miniature container 50, which may be constructed of a suitable material such as plastic. Container 50 includes casing 52, a threaded metal contact 54 and point contact 56. The container 50 may be inserted in a screw type socket 58 of the same type and size used to hold the glow lamp of prior art circuits, as shown in FIG. 3. The threaded metal contact 54 electrically connects one terminal of the starting circuit to a cathode of lamp 1 via the sidewall 57 of socket 58; the point contact tenninal connects the other terminal of the starting circuit to a cathode of lamp 1 via the base 59 ofsocket 58.

FIG. 2 shows the container in vertical section and the arrangement of parts therein including symmetrical switch 30,

diode 32, autotransformer l4, capacitor 26, and diode 22. One terminal of the starting circuit is electrically connected to contact 54. The other terminal of the starting circuit is electrically connected to contact 56. Thus the entire starting circuit of this invention may be contained within a miniature container 50 and inserted into a glow lamp-type socket 58 which is electrically connected across the cathodes 2, 3 of fluorescent lamp 1 (see FIG. 3). Thus it is possible to easily and quickly convert a fluorescent lamp appliance of the glow starter type to one of the instantaneous lighting type by substituting a starter container 50 for the glow lamp used in prior art starting circuits.

The present invention provides a starting system at reasonable cost for use in fluorescent lamp appliances, especially of the miniature type. Further, the operative temperature range for fluorescent lamp appliances is found to be widened by the starting circuit of this invention; experiments have confirmed that the light lights normally through a range of minus 20 to Wh|le a particular embodiment of this invention is shown above and described, it will be understood, of course, that the invention is not to be limited thereto, since many modifications may be made. It is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

lclaim:

l. A two-terminal circuit for lighting a fluorescent lamp from an AC voltage source comprising:

a. means coupling said AC source to the terminals of said lamp;

b. a unidirectional current conducting means;

c. a capacitor;

d. an autotransformer having a primary and a secondary, said secondary being coupled to said two terminals of said lamp through said unidirectional current conducting means and through said capacitor;

e. a unidirectional current conducting switching circuit means for conducting current in one direction when the voltage across said circuit exceeds a predetermined value;

f. said switching means being coupled between said capacitor and the primary of said transformer whereby said capacitor discharges into said primary when said switching means is conductive, thereby generating a starting pulse across the terminals of said lamp.

2. The circuit of claim 1 wherein said switching means includes a series combination of a diode and a silicon symmetrical switch.

3. The circuit of claim 1 wherein said means coupling the AC source to the lamp includes an inductive circuit element.

4. The two-terminal circuit of claim 1 further including a small container for said circuit, said container including a twoterminal plug adapted to fit into a two-terminal socket with terminals connected to the terminals of said lamp. 

1. A two-terminal circuit for lighting a fluorescent lamp from an AC voltage source comprising: a. means coupling said AC source to the terminals of said lamp; b. a unidirectional current conducting means; c. a capacitor; d. an autotransformer having a primary and a secondary, said secondary being coupled to said two terminals of said lamp through said unidirectional current conducting means and through said capacitor; e. a unidirectional current conducting switching circuit means for conducting current in one direction when the voltage across said circuit exceeds a predetermined value; f. said switching means being coupled between said capacitor and the primary of said transformer whereby said capacitor discharges into said primary when said switching means is conductive, thereby generating a starting pulse across the terminals of said lamp.
 2. The circuit of claim 1 wherein said switching means includes a series combination of a diode and a silicon symmetrical switch.
 3. The circuit of claim 1 wherein said means coupling the AC source to the lamp includes an inductive circuit element.
 4. The two-terminal circuit of claim 1 further including a small container for said circuit, said container including a two-terminal plug adapted to fit into a two-terminal socket with terminals connected to the terminals of said lamp. 